The present invention relates to a magneto-resistance effect type magnetic head in which a spin valve film is used as a magnetic sensing device for detecting a magnetic signal while contacting in sliding motion with a magnetic recording medium and a magnetic tape apparatus in which the magneto-resistance effect type magnetic head is incorporated.
A magneto-resistance effective device (hereinafter referred to as MR element) makes use of a magneto-resistance effect that the resistance value varies depending upon the magnitude and the direction of an external magnetic field. The MR element is used, for example, as an magnetic sensing device of a magnetic head or the like for detecting a signal magnetic field from a magnetic recording medium.
As such, an MR element as described above, a device is conventionally used wherein an anisotropic magneto-resistance effect is utilized. However, in such an MR element as just described, the magnetic resistance variation coefficient (MR ratio) is low. Therefore, an MR element having a still higher MR ratio is demanded. In recent years, a giant magneto-resistance effect device (hereinafter referred to as GMR element) in which a spin valve film is utilized has been proposed (refer to, for example, “Giant Magnetoresistance in Soft Ferromagnetic Multilayers”, Physical Review B, vol. 43, No. 1, pp. 1297-1300, which is hereinafter referred to as Non-Patent Document 1, and Japanese Patent Laid-Open No. Hei 8-111010, which is hereinafter referred to as Patent Document 1).
A GMR element includes a spin valve film wherein a nonmagnetic layer is sandwiched by and between a pair of magnetic layers and utilizes an effect called a giant magneto-resistance effect in which the conductance of sense current flowing in an in-plane direction in the spin valve film varies depending upon the relative angle of magnetization between a pair of magnetic layers.
In particular, the spin valve film is structured such that an antiferromagnetic layer, a fixed magnetization layer having magnetization fixed in a predetermined direction by an exchange coupling magnetic field acting between the antiferromagnetic layer and the fixed magnetization layer, a free magnetization layer having a magnetization direction which varies in response to an external magnetic field, and a nonmagnetic layer for magnetically isolating the fixed magnetization layer and the free magnetization layer from each other are laminated.
In the GMR element in which the spin valve film is used, if an external magnetic field is applied, then the magnetization direction of the free magnetization layer varies in response to the magnitude or the direction of the external magnetic field. Then, when the magnetization direction of the free magnetization layer is the opposite direction (anti-parallel direction) with respect to the magnetization direction of the fixed magnetization layer, the resistance value of the sense current flowing in the spin valve film exhibits its maximum. On the other hand, when the magnetization direction of the free magnetization layer is the same direction (parallel direction) as the magnetization direction of the fixed magnetization layer, the resistance value of the sense current flowing in the spin valve film exhibits its minimum.
Accordingly, in the magnetic head which includes such a GMR element as described above (a head of this type is hereinafter referred to as GMR head), where constant sense current flows to the GMR element, the voltage value of the sense current flowing in the GMR element varies in response to a signal magnetic field from a magnetic recording medium. Thus, if the variation of the voltage value of the sense current is detected, then the magnetic signal from the magnetic recording medium can be read.
Patent Document 1 discloses a GMR head utilized in a hard disk drive. The hard disk drive is structured such that the GMR head is carried on a head slider attached, for example, to an end portion of a suspension. While air flows generated by rotation of a magnetic disk make the head slider float above a signal recording face of the magnetic disk, the GMR head carried on the head slider reads out a magnetic signal recorded on the magnetic disk, thereby performing a reproduction operation for the magnetic disk.
In recent years, the utilization of the GMR head not only in a magnetic disk apparatus but also in a magnetic tape apparatus, such as a tape streamer has been and is being investigated. For example, a tape streamer to which helical scanning is applied is structured such that the GMR head is disposed on an outer circumferential face of a rotary drum such that it is inclined obliquely with respect to a substantially orthogonal direction to a feeding direction of a magnetic tape in accordance with an azimuth angle. Further, in the tape streamer, the rotary drum is driven to rotate while the magnetic tape is fed in an oblique direction with respect to the rotary drum, and the GMR head carried on the rotary drum slidably moves on the magnetic tape to read out a magnetic signal recorded on the magnetic tape, thereby performing a reproduction operation of the magnetic tape.
In the tape streamer, preferably, the distance between the GMR head and the magnetic tape, that is, the spacing, is minimized. Therefore, from a point of view of the spacing, preferably, the surface of the magnetic tape is smoothed.
However, as the surface of the magnetic tape is smoothed into a mirror face, the contact area between the magnetic tape and the outer circumferential face of the rotary drum increases. This increases the frictional force acting between the magnetic tape and the rotary drum during feeding of the magnetic tape to such a degree that the magnetic tape and the rotary drum stick to each other, thereby obstructing smooth feeding of the magnetic tape. Therefore, such a contrivance is applied in which very small projections are provided on the surface of the magnetic tape using a Siol filler or an organic filler to decrease the contact area between the magnetic tape and the outer circumferential face of the rotary drum, thereby decreasing the frictional force acting between the magnetic tape and the rotary drum. Further, a protective film, such as a DLC film or the like, for preventing damage, corrosion and so forth is formed on the surface of the magnetic tape.
Incidentally, in the hard disk drive described above, a reproduction operation is performed in a state wherein the GMR head does not contact the signal recording face of the magnetic disk. Further, Cu is normally used for the nonmagnetic layer which forms the spin valve film. Conventionally, a protective film, such as a DLC (Diamond Like Carbon) film or the like, for preventing corrosion of the Cu is formed on a medium opposing the face of the GMR head which opposes the magnetic disk.